This invention relates generally to the field of digitally controlled printing devices and methods, and in particular to continuous ink jet print heads and methods which integrate multiple nozzles on a single substrate and in which the breakup of a liquid ink stream into droplets is caused by a periodic disturbance of the liquid ink stream.
Many different types of digitally controlled printing systems have been invented, and many types are currently in production. These printing systems use a variety of actuation mechanisms, a variety of marking materials, and a variety of recording media. Examples of digital printing systems in current use include: laser electrophotographic printers; LED electrophotographic printers; dot matrix impact printers; thermal paper printers; film recorders; thermal wax printers; dye diffusion thermal transfer printers; and ink jet printers. However, at present, such electronic printing systems have not significantly replaced mechanical printing presses, even though this conventional method requires very expensive setup and is seldom commercially viable unless a few thousand copies of a particular page are to be printed.
Inkjet printing has become recognized as a prominent contender in the digitally controlled, electronic printing arena because of its non-impact, low-noise characteristics, its use of plain paper and its avoidance of toner transfers and fixing. Ink jet printing mechanisms can be categorized as either continuous ink jet or drop on demand ink jet. Continuous ink jet printing dates back to at least 1929. See U.S. Pat. No. 1,941,001 issued to Hansell.
U.S. Pat. No. 3,373,437, which issued to Sweet et al. in 1967, discloses an array of continuous ink jet nozzles wherein ink drops to be printed are selectively charged and deflected towards the recording medium. This technique is known as binary deflection continuous ink jet.
U.S. Pat. No. 3,416,153, which issued to Hertz et al. in 1966, discloses a method of achieving variable optical density of printed spots in continuous ink jet printing using the electrostatic dispersion of a charged drop stream to modulate the number of droplets which pass through a small aperture.
U.S. Pat. No. 3,878,519, which issued to Eaton in 1974, discloses a method and apparatus for synchronizing droplet formation in a liquid stream using electrostatic deflection by a charging tunnel and deflection plates.
U.S. Pat. No. 4,346,387, which issued to Hertz in 1982, discloses a method and apparatus for controlling the electric charge on droplets formed by the breaking up of a pressurized liquid stream at a drop formation point located within an electric field having an electric potential gradient. Drop formation is effected at a point in the field corresponding to the desired predetermined charge to be placed on the droplets at the point of their formation.
Conventional continuous ink jet utilizes electrostatic charging rings that are placed close to the point where the drops are formed in a stream. In this manner individual drops may be charged. In addition to charging rings, deflection plates having a large potential difference between them may be used to deflect drops which are charged downstream. Uncharged drops are not deflected.
In all such continuous ink jet printers, a gutter (sometimes referred to as a xe2x80x9ccatcherxe2x80x9d) intercepts ink drops not intended for printing. For example, charged drops may be deflected so as to miss the gutter and thereby pass on as print drops to a receiver, whereas uncharged drops are captured by the gutter.
U.S. Pat. No. 6,079,821, issued Jun. 27, 2000, discloses a continuous ink jet printer system in which heat is applied asymmetrically to an ink stream to control the direction of the stream between a print direction and a non-print direction. This method renders unnecessary the electrostatic charging tunnels of conventional continuous ink jet technologies and serves to better couple the functions of droplet formation and droplet deflection. However, the ink stream must be heated for deflection to occur.
The continuous ink jet printer described in accordance with the present invention eliminates the need for electrostatic charging systems and deflection plates in continuous ink jet printers without requiring the addition of heat to control the direction of the ink stream between a print direction and a non-print direction.
It is an object of the present invention to provide a high speed apparatus and method of page width printing utilizing a continuous ink jet method whereby drop formation and deflection may occur at high repetition.
It is another object of the present invention to provide an apparatus and method of continuous ink jet printing with a drop deflection mechanism which can be integrated with the print head utilizing the advantages of silicon processing technology offering low cost, high volume methods of manufacture.
It is another object of the present invention to provide an apparatus and method of high speed printing that can use a wide variety of inks.
It is yet another object of the present invention to provide an apparatus and method for continuous ink jet printing that does not require electrostatic charging plates.
It is still another object of this invention to provide a continuous ink jet printing system that integrates an ink stream deflection means into the nozzle of a continuous ink jet printer.
The invention, and its objects and advantages, will become more apparent in the detailed description of the preferred embodiments presented below.
There is provided by this invention a print head of the continuous ink jet type wherein multiple nozzles are fabricated into a silicon substrate. Annular heaters may be fabricated around the nozzles to create variable size drop formation in the ink stream. A notch in the nozzle bore having a predetermined width and adjustable depth accomplishes deflection of the drops for printing.